The present invention relates to a photothermographic material.
In recent years, reduction of amount of waste processing solutions is strongly desired in the field of medical diagnosis films and the field of photoengraving films from the standpoints of environmental protection and space savings. Therefore, techniques relating to photothermographic materials for medical diagnosis films and photoengraving films are required which enables efficient exposure by a laser image setter or a laser imager and formation of a clear black image having high resolution and sharpness. The photothermographic materials can provide users with a simple and non-polluting heat development processing system that eliminates the use of solution-type processing chemicals.
The same applies to the field of ordinary image-forming materials. However, photo-images for medical use require high quality excellent in sharpness and graininess as they need very fine images. In addition, for easy diagnosis, cold monochromatic images are preferred. At present, various types of hard copy systems using pigments and dyes, for example, ink jet printers and electrophotographic systems are available as ordinary imaging systems. However, no satisfactory image-forming system is available for medical images.
Photothermographic systems utilizing a silver salt of an organic acid are described, for example, in U.S. Pat. Nos. 3,152,904 and 3,457,075 and Klostervoer, xe2x80x9cThermally Processed Silver Systemsxe2x80x9d, Imaging Processes and Materials, Neblette, 8th ed., compiled by J. Sturge, V. Walworth and A. Shepp, Chapter 9, p.279, (1989). The photothermographic material, in particular, comprises a image-forming layer (photosensitive layer) containing a photocatalyst (e.g., silver halide) in a catalytically active amount, a reducing agent, a reducible silver salt (e.g., silver salt of an organic acid), and optionally a toning agent for controlling tone of silver, which are usually dispersed in a binder matrix. When the photothermographic material is heated at a high temperature (e.g., 80xc2x0 C. or higher) after light exposure, a monochromatic black silver image is produced through an oxidation-reduction reaction between the silver halide or the reducible silver salt (which functions as an oxidizing agent) and the reducing agent. The oxidation-reduction reaction is accelerated by catalytic action of a latent image of silver halide generated upon exposure. Therefore, the monochromatic silver images are formed in exposed areas of the materials. This technique is disclosed in many references including U.S. Pat. No. 2,910,377 and Japanese Patent Publication (Kokoku, hereinafter referred to as JP-B) 43-4924. The photothermographic systems using a silver salt of an organic acid can achieve image quality and tones that satisfy the needs in the medical filed.
For the photothermographic systems using a silver salt of an organic acid, it is one of important objects to improve storability of the photothermographic materials before image-wise light exposure. Organic polyhalogenated compounds are known as promising materials for improvement of the storability before light exposure. For development of materials, there are desired (1) low material cost, (2) good material safety and (3) reduced amount of a material to be used. Organic polyhalogenated compounds such as, for example, those described in Japanese Patent Laid-open Publication (Kokai, hereinafter referred to as JP-A) 9-258367, JP-A-54-165, JP-A-10-339934, JP-A-7-2781 and the like have been proposed. However, further improvement has been desired from a viewpoint of compatibility between sensitivity and storability.
An object of the present invention is to solve the aforementioned problems of the prior art. More specifically, the object is to provide a photothermographic material that can be used for medical images, photoengraving and the like and has high sensitivity and superior storability before light exposure.
The aforementioned object was achieved by the following means.
That is, the present invention provides a photothermographic material comprising, on one surface of a support, at least one kind of photosensitive silver halide, a silver salt of an organic acid, a reducing agent for silver ions, and a binder, wherein
(1) said material further comprises two or more kinds of organic polyhalogenated compounds, and
(2) a melting point of a mixture which consists of the organic polyhalogenated compounds in the same content ratio as the content ratio of said compounds in the photothermographic material is in the range of from xe2x88x9210xc2x0 C. to 50xc2x0 C. relative to a heat development temperature for the photothermographic material.
According to a preferred embodiment of the present invention, there is provided the aforementioned photothermographic material, wherein the photothermographic material is formed by coating an aqueous coating solution on the support, and wherein the organic polyhalogenated compounds are added to the aqueous coating solution in a dispersed state.
The photothermographic material of the present invention has high sensitivity and superior storability before heat development, and the material can be used for medical images, photoengraving and the like.